The present disclosure relates to incontinence detection systems and particularly, to incontinence detection systems that use a pad beneath a person lying in a patient bed. More particularly, the present disclosure relates to incontinence detection systems that are able to communicate wirelessly between the pad and a reader on the patient bed.
Incontinence detection systems that have incontinence detection pads placed beneath a patient on a patient bed are known. For example, U.S. Pat. No. 5,537,095 discloses an incontinence detection pad having electrical circuitry that couples via a wired connection to a controller of a patient bed. Recent efforts have involved the development of wireless communication between the circuitry of the incontinence detection and a reader on a patient bed. The antennae in some such prior systems are individually powered by a reader to energize a passive RFID chip on the incontinence detection pad and to read backscattered data sent from the passive RFID chip back to the reader via the antennae.
In the known wireless incontinence detection pad systems, signal to interfere (S/I) ratio issues are prevalent. For example, when a monostatic architecture using a hybrid directional coupler to provide receiver isolation from the transmitter and to allow simultaneous transmission and reception on the same antenna, the coupling between the transmitter and receiver ports of the hybrid coupler is about −10 decibels (dB). This means that 90% of the received signal does not end up in the receiver. Furthermore, if the antenna impedance deviates from the transmission line characteristic impedance, the power reflected from the antenna is coupled into the receiver input and is much stronger than the backscattered signal from the RFID tag, which creates the situation where the receiver must reject a very strong signal near the signal of interest in order to detect and demodulate only the signal of interest, which in the case of an EPC 2 compliant tag, is 256 kilohertz (kHz) away from the carrier. In such situations the S/I ratio can be on the order of 50 dB. An alternative known architecture is the use of a circulator which couples the transmitter and receiver, functionally, in a similar way as a hybrid coupler. However, the S/I ratio using a circulator is only about 1.6 dB better than the hybrid coupler approach.
Other interfering signals include forward power coupling into the receiver port, which can be 5 dB higher than the tag backscattered signal, and power reflected from the RF forward power, which can be 34 dB stronger than the backscattered signal. All of these signals add into the front end of the receiver, which subjects it to overload and intermodulation distortion products which may further impact the performance of the receiver. In other words, because there is a strong signal close in frequency to a weak signal, it is difficult to detect the weak signal. A further concern is that RFID systems that are located in close proximity to a patient's body experience communication channel degradation due to the interaction of the biological tissue and body fluids with the RFID tag.
Based on the foregoing, it should be apparent that there is an ongoing need for improved electrical architecture in wireless incontinence detection pad systems used on patient support apparatuses such as patient beds.